Cooling systems in current internal combustion engines are designed to protect engines from exceeding maximum allowable temperatures during engine operation. Such systems normally incorporate controls such as thermostats, shutters, fan clutches and the like, as a manner of controlling minimum engine temperatures and engine operating temperatures in relation to the ambient temperature conditions and power output requirements of the engine. In such prior systems, the coolant normally approaches elevated temperatures only when the engine is operating in high ambient temperatures, and at or near full power. Thus, a direct relationship exists between the coolant temperature and the engine coolant demands. As a result of such a relationship the operating efficiency of the engine is significantly reduced when the engine is operating at a part load or less condition and in a moderate to low ambient temperature range. Since many engines are normally operated under such conditions for prolonged periods of time fuel consumption is inordinately high and coolant dependent accessories such as cab heaters and the like operate less efficiently. In an attempt to overcome these problems, sophisticated and costly controls are employed in some prior cooling systems.